The present invention relates to information extraction for Doppler radar systems, and more particularly to a filter array for such systems.
In Doppler radar systems, the return pulse reflected back from a moving target contains information indicating the presence of the target and the radial velocity of the target relative to the transmitter. Extraction of the first type of information, that is, the presence of a target, is relatively simple and this is often the only type of information desired. When information as to the velocity of the target is also required, however, complex and expensive schemes have heretofore been necessary.
The velocity information contained in a return radar pulse reflected from a moving target involves a change in frequency of the return pulse which is related to the frequency of the transmitted pulses and to the radial velocity of the target. The frequency, or frequency change, of the return pulse must, therefore, be detected to extract the desired information, and this has been done by means of banks of filters responsive to contiguous frequency bands. The return signal is applied to the filter bank and the frequency is determined by identifying the filter which passes the signal. The desired velocity of the target can then be calculated from this information. The velocity information extraction systems used heretofore, therefore, have involved the use of banks of contiguous filters with isolation networks between them, or crystal sharing filter banks which require active networks or digital processing techniques. Such systems are very complex and are difficult and expensive to produce, and are also wasteful of either signal energy or primary energy.